Method of reducing high temperature embrittlement of titanium alloys



METHOD OF REDUCING HIGH EERATURE EMBRITTLEMENT F TlTe -i ALLOYS William W. Gullett, College Park, Mi, assignor to (Illicago Development Corporation, Riverdale, Md.

No Drawing. Application April 18, 1955, Serial No. 502,200

2 Claims. (Cl. 7S175.5)

This invention relates to titanium alloys. It relates particularly to the stabilization of alloys containing minor amounts of interstitial solutes. In my co-pending application, Serial No. 439,160, filed June 17, 1954, of which this application may be considered a continuation in part, I have disclosed the procedure of stabilizing the alloys with respect to their interstitial content. It will be understood that by stabilization I mean to define a condition in which the activity of the interstitial solutes is substantially reduced, that is, the effects on properties produced by a given total concentration of the interstitials is considerably lessened.

I have found that very small amounts, less than .10%, of barium added to titanium reduces the activity of the interstitials present in commercial titanium to a very low level when properly heat treated. I have found that the best heat treatment for this purpose consists in heating the alloys for a short period at 800 C. and quenching. It should be pointed out that this treatment does not irreversibly stabilize the alloys. The activity of the interstitials may be restored by heating to 400 C. The addition of barium, in accordance With my invention, is therefore efiective only at relatively high temperatures. This increase in stabilization at high temperatures is the reverse of stabilization with some other alloying additions, notably aluminum and manganese. Consequently, the addition of barium to alloys of manganese and aluminum produces an overall stabilization since the barium stabilizers the interstitials at high temperatures, and the other alloying elements stabilize them at loW temperatures. As a result, the addition of barium to these titanium alloys makes them markedly less sensitive to rate of cooling and provides alloys which can be subjected to almost any heat treating schedule without embrittlement.

The addition of a significant amount of barium to titanium alloys has heretofore been diflicult since if added to molten titanium in the arc, it vaporizes to a major extent. I have found that barium-titanium alloys pro- Y duced by electrolysis of barium and titanium chlorides do not lose barium so rapidly when arc melted, and the amount of barium necessary for my invention can be readily added to titanium and titanium alloys by adding 10-20% of such electrolytically produced alloy. The amount of barium added in this way is not critical since any excess over about 0.1% Will be vaporized in melting. It will, however, have remained in the melt long enough to remove some oxygen.

In the following table I have illustrated several alloys made in accordance with my invention. These alloys were melted in an arc furnace with a water cooled hearth and a tungsten electrode. The titanium used was in the form of fragments of cathode plate produced by electrolysis of an electrolyte containing barium chloride, sodium chloride and titanium chloride. These fragments contained 0.2% barium. The alloying metals were added as such and the ingots were forged at 1700 F. and rolled to rods.

The oxygen activity is determined in accordance with the method set forth in my co-pending application. That is, the alloy is made the anode in a compartment cell 2 having an electrolyte of lithium and potassium chloride. When the catholyte is saturated with lithium, the voltage of the cathode against the alloy is measured. This voltage measures the oxygen activity according to the following table:

Difi. From Percent Active 01 Pure Tl,

Volts with the alloys the difierence from pure titanium is determined, and this is converted to active oxygen in accordance with the table. The oxygen activity is then the active oxygen divided by the total oxygen.

The impact strength is expressed in foot-pounds as determined on a Charpy machine.

The temperatures indicated in the table are those to which the alloys have been heated for 1 hour, then air cooled:

I have illustrated my invention with barium, but I have found that strontium may be substituted in every instance with the same results.

What is claimed is:

l. The method of reducing high-temperature embrittlement of titanium alloys containing about 0.1% oxygen, which consists in adding to such oxygen-containing alloy, during melting, a second titanium alloy of the group consisting of titanium-barium and titanium-strontium alloys, said second titanium alloy being added in an amount corresponding to about 0.1% of the alloying metal of said second titanium alloy, whereby to substantially eliminate embrittlement of the resulting alloy by quenching from about 800 C. after casting and fabrication.

2. The method of reducing high-temperature embrittlement of titanium alloys containing about 0.1% oxygen, and at least one alloying element of the group consisting of manganese, aluminum and chromium, which consists in adding to such oxygen-containing alloy, during melting, a second titanium alloy produced by the electrolysis of a fused salt bath containing chlorides of titanium and a metal of the group consisting of barium and strontium, said second titanium alloy being added in an amount corresponding to about 0.1% of said metal, whereby to substantially eliminate embrittlement of the resulting alloy by quenching from about 800 C. after casting and fabrication.

References Cited in the file of this patent UNITED STATES PATENTS 2,675,309 Vordahl Apr. 13, 1945 

1. THE METHOD OF REDUCING HIGH-TEMPERATURE EMBRITTLEMENT OF TITANIUM ALLOYS CONTAINING ABOUT 0.1% OXYGEN, WHCH CONSISTS IN ADDING TO SUCH OXYGEN-CONTAINING ALLOY DURING MELTING, A SECOND TITANIUM ALLOY OF THE GROUP CONSISTING OF TITANIUM-BARIUM AND TITANIUM-STRONTIUM ALLOYS, SAID SECOND TITANIUM ALLOY BEING ADDED IN AN AMOUNT CORRESPONDING TO ABOUT 0.1% OF THE ALLOYING METAL OF SAID SECOND TITANIUM ALLOY, WHEREBY TO SUBSTANTIALLY ELIMINATE EMBRITTLEMENT OF THE RESULTING ALLOY BY QUENCHING FROM ABOUT 800*C. AFTER CASTING AND FABRICATION. 